Apparatus fob making magnetic



June 4, 1935. P. c. HERMANN 19,600

' APPARATUS FOR MAKING IAGNETIC TESTS AND MEASUREMENTS Original Filed Aug. 18, 1932 Inventor Peter C. Hermann,

1 WM 7 His Attdrney.

Reissued June 4, 1935 APPARATUS FOR MAKING MAGNETIC TESTS AND MEASUREMENTS Peter 0, Hermann, Berlin-Zehlendorfehfltte,

Germany, assignor to General Electric Company, a corporation of New York Original No. 1,925,812, dated September 5, 1933,

Serial No. 829,369, August 18, 1932. Application for reissue February 6, 1935, Serial No.

5 claim.

My invention relates to apparatus for making magnetic tests and measurements and concerns particularly an arrangement suitable for testing different materials under working conditions. In the laboratory magnetization curves may readily be determined for the purpose of ascertaining the characteristic magnetic constants such as coercive force, remanence, initial and maximum permeability, hysteresis losses and saturation, and the like. Accurate results may be obtained bycarrying out the measurements on a closed ring. The laboratory method utilizing-a closed ring, however, isnot suitable when the tests are to be carried out under working conditions continuously or when it is desired to take repeated measurements on a piece of sheet metal in order to determine the thermol eflects, for

example.

The necessity for the use of a closed ,ring has been overcome in certain types of apparatus by building up. cores from test strips arranged in layers in a closed form, or by utilizing aclosing yoke. However, the accuracy of the apparatus and the uniformity of the results is interfered with by the presence of the free poles formed at the abutting joints-which tend to demagnetize the magnetic material.

It is an' object of my invention to provide an apparatus in which the difilculties of the prior devices are overcome by magnetizing the sample in a free 0011 and taking a direct measurement of the eflective field strength. It is a further ob-' ject of my invention to provide an apparatus in which tests may be made upon small quantities of test material in shapes that may be obtained easily, particularly fiat strips or sheets. In accordance with my invention in its prefen-ed form the sample in the form of a strip ofsheet metal is surrounded by a magnetizing winding. The width of the strip is so great that the efifect of any hardening of the edge is negligible. The operation of my device depends upon the principle that the actual efi'ective field strength in the metal strip is just as great as the field strength in the air'at the surface of the -metai. This law is based upon the continuity of the tangential component of the field strength hen passing to the outside layers.

One or two filamentary conductors are mounted in close proximity to the surface of the test strip and the deflection of thefilaments when a current is passed through provides an indication.

n! the of field at the surface of the magnetic test strip. Any suitable means such as a microscope used to observethe motion of the In Germany September 1, 1931 filaments or a rotating mirror carried'by the pair of filaments in the manner of an oscillograph loop may be employed in conjunction with an optical system in order to provide an indication of the bending of the filaments therebyproviding an indication of the strength of field. The features of my invention which I believe to be novel and patentable-will be pointed out in the claims appended hereto.

For a more complete understanding of my invention reference may be had to the accompanying drawing in which Fig. 1 is a longitudinal section cut by a plane l -l through the magnetizing winding; Fig. 2 represents a cross section cut by the plane 2-2; and Fig. '3 is a schematic diagram partly in section of one embodiment of my invention.

Referring now more in detail to the drawing in which like reference characters-refer to like parts throughout, I provide a cylindrical magnetizing 20 winding ll energized by any suitable source of current such as a battery l2. Test piece It is placed in magnetic relation to the magnetizing winding ll. Preferably the test piece It takes the form of a flat strip supported within the winding by a nonmagnetic frame It.

In order to provide a direct indication of the field strength within and at the surface of the test piece it, a current-conducting filament I5 is mounted in close proximity to the surface of the test piece 13. Although I am not limited to this specific arrangement, I prefer to employ apair of parallel filaments l5 and it connected injseries at one end. A suitable source of current, such as,

for example, a battery B in series with a currentcontrolling rheostat R and an ammeter A is connected to the terminals l1 and II which supply the filaments IS and It with direct current. Current'fiows in opposite directions in the two filaments so that they are deflected in opposite di- 40 rections.- A mirror I! is'supported by the filaments l5 and' It and cooperates with a suitable device 20 such as a mirror or prism, a source of light 2| and a scale 22 to provide an indication of the deflection or the filaments Is and Is in response to the reaction between the current fiowing in the filaments and the magnetic field at the surface of the test piece It. Itwill be understood that the current in the filament l5, I8 ismaintained at a predetermined value dining a readin by means of the rheostat R. The filament l5, l8 islocatedinafieldwhichissoclosetothesurface of the magnetic test piece II as to be' substantially unchanged from the field within the test piece. Consequently the deflection of the filaments l5 and It provides a direct indication of the field strength. In my apparatus, corrections which would have to be made in calculating the field strength from the magnetizing current are therefore rendered unnecessary. ,f'In order that measurements of the magnetic induction in the iron mayalso be taken, I-provide ,an induction measuring coil 23 cooperating with a ballistic galvanometer 24 in the customary manner. A compensation coil 25 may in some cases be desirable as when the cross section of the test piece I3 is small compared 'with the air cross section of the magnetizing winding II. When the compensation coil 25 is employed, it may be arranged in any desired manner for compensat-' ing or overcoming the efi'ect of stray or leakage field. For example, it may be connected in sefies-opposition with the induction-measuring coil 23 in the manner well understood by those skilled'in the art. The induction measurement winding 23 is placed as close as possible to the point at which the field Strength is measured so that the induction and the field strength is measured at practically the same point. By this means all faults due to stray fields are avoided and measurements are not taken of average values for the sample which is generally unevenly magnetized, but the measurements are obtained of the actual values for induction and field strength which are associated with one another,

in a small portion which may be regarded as being evenly magnetized. Calibration of the field measuring apparatus may easily be carried out at any time by'examining the relation of the magnetizing current and the field deflection without any ferrmmagnetic material. When the data for the magnetizing coils are taken into consideration, a calibration constant for the apparatus can ined. t ccordance with the provisions of the patbe obt en statutes I, have described-the principle of opi-ation of my invention together with the app'aratus which I now consider torepresentthe' best embodiment thereof, but I desire to have it understood that the apparatus shown 'is only illustrative and that the invention may be carried out by-other means.

"What I claim as new and desire to secure by f Letters Patent of the United States, is:

1. Ap iratus for making magnetic measure ments'jormagneuc samples having fiat surfaces,

' comprising a magnetizing winding, means for supporting such a sample in testing position in magnetic relation with said winding,-a flexible current conductor supported in said winding so as to be parallel with and in relatively close proxim ity to the surface of a sample in testing position,

and means for. supplying" an electrical current to .said conductor to cause a deflection of said conductor and an indication of the'strength of the magnetic field in the sample under test.

'- 2. Apparatus i'or making magnetic measurements or test pieces in the form of fiat strips.

comprising a magnetizing winding-arranged to surround such a test piece, means for energizing said winding, a current conducting filament supported transverse the axis 01 said magnetizing winding so as to be parallel with and in relatively .close proximity to one surface of a piece in testing position, means for supplying an electric current to said filament, said filament being deflectedin accordance with the magnetic field strength to which the piece under test is subjected, thereby prclividing a direct response to the strength'of said fie d.

3. Apparatus for making magnetic measurements of test pieces having .fiat surfaces, compris ing a magnetizing winding arranged to surround such a test piece, means for energizing said wind: ing, a pair of current conducting filaments connected in series supported transverse to the axis of said magnetizing-winding so as to be parallel with and in relatively close proximity to the surface of apiece in testing position, said pair of filamentsbeing twisted in accordance with the magnetic field strength to which the test piece is subjected thereby providing a-direct response to the strength of said field. 4. Apparatus for making magnetic measurements of magnetic samples having. flat surfaces, a magnetizing winding arranged to surround such a sample, means for-energizing sa'id winding, a' v pair of parallel current conducting filaments ,con-

nected in series supported transverse to the axis of said magnetizing windingso asto be parallel with and in relatively close proximity to one sur-' face of a sample in testing position, means for.

their'enda'said filaments being oppositely defiected in accordance with the magnetic field strength to which the sample under test is subjected, thereby rotating said mirror in direct response to the strength of said field, and an optical systemre- 'sponsive to the-rotation of said mirror.

5. Apparatus for making magnetic measurements or a magnetic sample in the form of a fiat strip, a magnetizing winding arranged to surround such a sample, means for energizing said winding, a current conducting filament supported transverse the axis of'said magnetizing winding so as to be parallel with and in relatively close proximity to one surface of a sample intesting, position, means for supplying an electric current to-said filament, said filament being deflected in accordance with the magnetic field strength to which the sample under test is subjected, an induction-responsive coil in inductiverelation with the sample under test'with its magnetic axis parallel tothe sample and to the axis of said mag-- netlzing winding, means responsive. to change in induction through said coil whereby the field strength and the induction in a-given portion of asamplemaybemeasuredmaniac, 

